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Old 20-01-2019, 09:13   #1
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Dyneema vs nylon for cat mooring pendant

I've seen a lot of discussion regarding bridles and pendants in general, but haven't seen anything on opinions regarding optimum material for both the mooring pendant and the bridle that attaches to it. This picture from West Marine's "How To" page suggests a nylon pendant and Dyneema bridle lines are the way to go. The text that goes with it describes the shock absorbing ability of the nylon pendant.

I'm wondering if the opposite is better. Since the pendant is the single source of failure item, shouldn't it be Dyneema? The bridles are independent of themselves since I always use 2 lines--one for each side, through the pendant eye back to the same cleat on the cat's bows. Nylon bridles can then do the shock absorbing work in the setup.

Interested in thoughts. Thanks.
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Old 20-01-2019, 09:28   #2
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Re: Dyneema vs nylon for cat mooring pendant

I'd guess the cafe where the bridle goes over the chock/cleat is why they spec'd dyneema there.

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Old 20-01-2019, 09:47   #3
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Re: Dyneema vs nylon for cat mooring pendant

Because Dyneema (or polyester) does not stretch, the movement back and forth across the chock is much less. Only a short strop is required to provide this benefit.


I would also use a chafe guard. Chafe Pro and Goyer Marine are good, as is tubular climbing webbing.
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Old 20-01-2019, 13:49   #4
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Re: Dyneema vs nylon for cat mooring pendant

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Originally Posted by thinwater View Post
Because Dyneema (or polyester) does not stretch, the movement back and forth across the chock is much less. Only a short strop is required to provide this benefit.


I would also use a chafe guard. Chafe Pro and Goyer Marine are good, as is tubular climbing webbing.
Since I take the bridle direct to the cleats on my bow cross beam, the lines do not go thru a chock or fairlead so I figure the chafe chances are lessened. However, any chafe at the cleats would still be present with nylon bridle lines...much less so with dyneema.
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Old 20-01-2019, 14:02   #5
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Re: Dyneema vs nylon for cat mooring pendant

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Since I take the bridle direct to the cleats on my bow cross beam, the lines do not go thru a chock or fairlead so I figure the chafe chances are lessened. However, any chafe at the cleats would still be present with nylon bridle lines...much less so with dyneema.
Just MHO, but the crossbeam is not designed to withstand great forces, and as your bridle is bearing the full weight of your vessel multiplied by its velocity from wind and waves at any given time, a makeshift bridle for a mooring would be more safely run between the forward deck cleats.
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Old 21-01-2019, 11:20   #6
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Re: Dyneema vs nylon for cat mooring pendant

Dyneema does not stretch, but it does creep. I have Dyneema for the stays on my sprit and for my lifelines on my 38ft. cat and it takes about three times to tighten them to get all the creep out of this hollow core rope. With Dyneema slack, as per for a mooring pennant, there will always be lots of creep, a sort of 'stretch'.
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Old 21-01-2019, 18:35   #7
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Re: Dyneema vs nylon for cat mooring pendant

Would be inclined to use nylon for both to get the max shock absorbency. Usually you would not have a very long pendant so even with nylon it will not have that much give. To prevent chafe on the bridal run a length of garden hose over the line and lash it in place. Since this is a dedicated rope chafe will always be in the same place so protection is easy.
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Old 21-01-2019, 18:59   #8
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Re: Dyneema vs nylon for cat mooring pendant

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Dyneema does not stretch, but it does creep. I have Dyneema for the stays on my sprit and for my lifelines on my 38ft. cat and it takes about three times to tighten them to get all the creep out of this hollow core rope. With Dyneema slack, as per for a mooring pennant, there will always be lots of creep, a sort of 'stretch'.
Creep only happens when Dyneema is loaded to a certain percentage of BL for a certain amount of time. With a dyneema bridle there should be no creep--it's not like mooring gear is under perpetual high tension. I like to have a short dyneema piece that goes from the bitts to the hawsehole or chock, then attach the nylon pennant there.
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Old 21-01-2019, 19:03   #9
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Re: Dyneema vs nylon for cat mooring pendant

My experience is that nylon rope is not the best in high UV areas, we tend to use "silver rope" (which I think is polypropylene) in a larger diameter
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Old 21-01-2019, 19:15   #10
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Re: Dyneema vs nylon for cat mooring pendant

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Originally Posted by Paul Howard View Post
Dyneema does not stretch, but it does creep. I have Dyneema for the stays on my sprit and for my lifelines on my 38ft. cat and it takes about three times to tighten them to get all the creep out of this hollow core rope. With Dyneema slack, as per for a mooring pennant, there will always be lots of creep, a sort of 'stretch'.
What you experienced when you tightened them thrice is called constructional stretch. Most of that was from your splices and the weave settling in. Creep is when the dyneema is loaded to a certain level of constant tension it elongates a certain amount over an extended period of time.
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Old 21-01-2019, 19:45   #11
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Re: Dyneema vs nylon for cat mooring pendant

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Originally Posted by roland stockham View Post
Would be inclined to use nylon for both to get the max shock absorbency. Usually you would not have a very long pendant so even with nylon it will not have that much give. To prevent chafe on the bridal run a length of garden hose over the line and lash it in place. Since this is a dedicated rope chafe will always be in the same place so protection is easy.
Your approach is proven to fail. @thinwater and @funjohnson have it right.
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Old 21-01-2019, 19:51   #12
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Re: Dyneema vs nylon for cat mooring pendant

Quote:
Originally Posted by Paul Howard View Post
Dyneema does not stretch, but it does creep. I have Dyneema for the stays on my sprit and for my lifelines on my 38ft. cat and it takes about three times to tighten them to get all the creep out of this hollow core rope. With Dyneema slack, as per for a mooring pennant, there will always be lots of creep, a sort of 'stretch'.

If there were actually significant true creep, Dyneema standing rigging would be impossible, but it is possible. What you are seeing is construction stretch and splices settling in. Colligo avoids this by using heat-set DUX and stretching the splices HARD before installing the rigging.

Others have stated the rest.
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Old 21-01-2019, 20:56   #13
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Re: Dyneema vs nylon for cat mooring pendant

Nylon. You picture a mono, but on a cat you keep the mooring lines VERY short and centered below your anchor or in light or no wind at all the mooring ball keeps banging against your hulls. Actually, your bridle is your mooring line. My cleats are beside the beam, never seen a chafe problem since 1998
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Old 22-01-2019, 03:37   #14
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Re: Dyneema vs nylon for cat mooring pendant

You need something with a bit of stretch to stop snatching the anchor out of its position in the sea bed. Dyneema is light--you need the weight of chain and lots of it for security, and nylon or polypropylene heavy ropes connected to the marker buoy and anchor chain for comfort in a blow. Vessels coming to a sudden abrupt halt after surfing backwards down a wave may well rip the bow cleats or chain locks right out of the deck--leaving the vessel to founder.

Nylon warps or rodes are wonderfully strong and elastic but not resistant to abrasion, so nylon has to be eye-spliced using a locked splice and many tucks into a stainless thimble, ( I put heavy heat-shrink plastic on the main rope first, then slide it over the finished splice and shrink it down, so that the ends and the entire splice are covered.) Where the nylon snubber comes aboard, the snubber needs to be encased in heavy polythene or polypropylene pipe guides, so the nylon never gets to rub on anything.
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Old 22-01-2019, 06:10   #15
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Re: Dyneema vs nylon for cat mooring pendant

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You need something with a bit of stretch to stop snatching the anchor out of its position in the sea bed. Dyneema is light--you need the weight of chain and lots of it for security, and nylon or polypropylene heavy ropes connected to the marker buoy and anchor chain for comfort in a blow. Vessels coming to a sudden abrupt halt after surfing backwards down a wave may well rip the bow cleats or chain locks right out of the deck--leaving the vessel to founder.

Nylon warps or rodes are wonderfully strong and elastic but not resistant to abrasion, so nylon has to be eye-spliced using a locked splice and many tucks into a stainless thimble, ( I put heavy heat-shrink plastic on the main rope first, then slide it over the finished splice and shrink it down, so that the ends and the entire splice are covered.) Where the nylon snubber comes aboard, the snubber needs to be encased in heavy polythene or polypropylene pipe guides, so the nylon never gets to rub on anything.

All well and good, but missing the point. The addition of a short Dyneema section where the pennant comes aboard eliminates the stretch (and abrasion) where it contacts cleat and chocks. Dyneema is also the most chafe-resistant of all rope materials. It is an advance over the construction you describe.

Nylon's stretch is what allows movement over the chocks and cleats, and even small movements cause abrasion and heat build-up in the core. In a big storm with strong repetitive pulls from wave action, the heat can be enough to cause melting at the rope's center, and failure. Braided polyester chafe coverings are better than plastic because they allow moisture to help cool the line. It would be even better to not have chafe at all: Hence the advance to adding a section of Dyneema.
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